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    Subject[PATCH 3.11 045/182] virtio_balloon: don't softlockup on huge balloon changes.
    Date
    3.11.10.9 -stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Rusty Russell <rusty@rustcorp.com.au>

    commit 1f74ef0f2d7d692fcd615621e0e734c3e7771413 upstream.

    When adding or removing 100G from a balloon:

    BUG: soft lockup - CPU#0 stuck for 22s! [vballoon:367]

    We have a wait_event_interruptible(), but the condition is always true
    (more ballooning to do) so we don't ever sleep. We also have a
    wait_event() for the host to ack, but that is also always true as QEMU
    is synchronous for balloon operations.

    Reported-by: Gopesh Kumar Chaudhary <gopchaud@in.ibm.com>
    Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
    Signed-off-by: Luis Henriques <luis.henriques@canonical.com>
    ---
    drivers/virtio/virtio_balloon.c | 6 ++++++
    1 file changed, 6 insertions(+)

    diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
    index 1f572c0..cfda0a6 100644
    --- a/drivers/virtio/virtio_balloon.c
    +++ b/drivers/virtio/virtio_balloon.c
    @@ -312,6 +312,12 @@ static int balloon(void *_vballoon)
    else if (diff < 0)
    leak_balloon(vb, -diff);
    update_balloon_size(vb);
    +
    + /*
    + * For large balloon changes, we could spend a lot of time
    + * and always have work to do. Be nice if preempt disabled.
    + */
    + cond_resched();
    }
    return 0;
    }
    --
    1.9.1


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